1. Field of the Invention
The present invention relates to an improved uninterruptible power supply circuit which uses an active flyback circuit to eliminate the remaining electromotive force in the transformer, to reduce heat loss during a flyback cycle, and to increase the safety of the uninterruptible power system; and also to an uninterruptible power supply circuit which uses an intelligent fast-charging circuit to achieve higher efficiency charging and to reduce the charging time.
2. Description of Related Art
At present, uninterruptible power systems (abbreviated as UPS) are very popular because many machines do not tolerate sudden power interruptions. For example, if power to a computer terminal is suddenly interrupted, important data may be lost. As a result, many kinds of UPS have been developed for the market. The present invention is an improvement over the conventional UPS. The technical contents of the present invention are different from that of co-pending application U.S. 08/327,935, filed on May 4, 1994.
One of the disadvantages of the conventional UPS has to do with the increasing use of microprocessors and digital circuitry, which are subject to problems of electromagnetic interference (abbreviated as EMI), electromagnetic susceptibility (abbreviated as EMS), and electromagnetic compatibility (abbreviated as EMC), and which are not adequately addressed by the conventional UPS.
As shown in FIG. 1, the conventional UPS adds capacitor C1, capacitor C2, and capacitor C3 to the input filter circuit of the power supply in order to reduce interference from electrical induction, but adding capacitor C1, capacitor C2, and capacitor C3 creates a capacitive reactance (Xe=1/2.pi.fc) in the circuit, and the output value of the voltage is reduced. Thus, it is necessary to enlarge the capacitor C1, capacitor C2, and capacitor C3 in the conventional UPS in order to reduce the capacitive reactance in the circuit, but enlargement of the capacitor in the input filter circuit not only increases the load on the UPS flyback circuit, it also usually causes damage to the UPS.
On the other hand, the charging circuit of the conventional UPS uses a constant voltage (13.7 V) and a constant current (0.5 A) to provide continuous but slow charging, requiring ten hours to fully charge. This is disadvantageous because when continuous charge is supplied to the battery, the voltage will fluctuate since the voltage at the charging terminal will be higher than the voltage of the uncharged terminal, reducing the charging current and further prolonging charging time. As a result, the charging time of the UPS battery is excessive, causing the battery to be overcharged and reducing the working life of the battery.